I would guess that if a circuit was published online that it is not "secret".
The only exception might be if a circuit is patented, but you could look that up.
You could still use the patented circuit as you see fit, you just couldn't make any money on it.
Let's see what the experts say...

Ok thanks for the info. The reson I ask is that I am designing a circuit board for work and I saw circuit online that was also a PCB that I liked.
The circuit I saw will be a different frequencies and different passive components also.
I just liked the method they used to detect capacitance.

If you would feel better paying a royalty check to someone for each board you produce, I would be happy to send you my address. I think $20/board would insure you don't feel guilty using someone else's design.

I'm just wondering is using a circuit found online as a starting point of a project for personal and proffesional work illegal?

Click to expand...

I don't want to be sarcastic but if you write "proffesional" on the PCB well uhm yes you know...

Most circuits online are technical level from the 1960s or 1970s, pretty much standard technology which is well known.

They are simple circuits, too.

You can use almost any schematic you encounter online.

I must also warn you many of them simply will not work, don't build any circuit from the internet when you don't understand it. Especially don't order 50,000 PCBs and then have to dump them.

Many circuits now use a digital firmware.

1) This is often not supplied. If it is supplied, only as HEX file. Which is often useless, as it ties you to a controller + you can not change the circuit.

2) Ripping it from a board of course is illegal. This is however so bad not many people have really ripped firmwares + built clones. People who cloned for instance Super Nintendo also had insider knowledge. They DID NOT simply read out the PROMS + traced the PCB tracks. It is a shady business.

So the schematic that I showed is a standard way of doing what I just explained to detect capacitance?
I dont have much experience on circuit board design most of my experience is in control systems. Only have been out of college for 3 years now.